There are many advantages to producing tires with a smooth tread surface. Some tire companies produce their products using the ‘puzzle’ and ‘vacuum’ mold methods. The purpose of this invention is to produce tires with a smooth surface by venting the tire molds differently with a more economically desired and manufactured mold. This new method of venting will eliminate the offensive appearing rubber protrusions (nubbins) from the tread portion of a tire caused by drilled vents in prior art tire molds.
Prior art “ventless” molds are built by a technique known as a puzzle mold. In those, small die cast pieces are made and assembled together in sections in the lateral (or transverse) direction of the tire. In the molding process air escapes through the cavities that are formed when the die cast pieces are placed together. This mold construction is always a segmented mold, expensive, complex and time consuming.
Also, the tread area of presently used molds, both 2-piece clamshell and segmented, are air vented by means of round vents located in strategic locations in the interior mold tread surface and drilled through the mold to the exterior atmosphere. The uncured tread rubber is pressed against the cavity of the tread of the mold under great pressure and heat. When the air escapes from the mold, rubber is pressed into the drilled vents leaving rubber protrusions (nubbins) sticking out of the tire when the tire is released from the mold. Over time some of these rubber protrusions (nubbins) will break off in the mold and will not permit the air to escape, causing the rubber not to fill the tread cavity completely. This is called rubber lightness or non-fill. The mold is necessarily then removed from production and cleaned. The typical cleaning operation uses a drill to clean the rubber from each vent; a very time consuming procedure because there are usually 1500 to 3000 vents per mold.
Also, before shipment a tire label may be placed on each tread surface. Many times labels will not stick to the tire because these protrusions (nubbins) will not permit the label to adhere to the surface of the tire.